CUET UG Biology Booster Test 2-Microbes in Energy and Biocontrol -

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CUET UG Biology Booster Test 2-Microbes in Energy and Biocontrol

⏱️ 30 Minutes

❓ 20 Questions

📌 Answers are locked once submitted — results and explanations appear at the end.

CUET UG Biology Booster Test 2-Microbes in Energy and Biocontrol

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QUESTION 1 OF 20

If a researcher notices that a specific batch of organic waste fermentation is yielding mainly carbon dioxide and virtually no methane, what is the most likely biological reason based on NCERT principles?

Answer Review

1 If a researcher notices that a specific batch of organic waste fermentation is yielding mainly carbon dioxide and virtually no methane, what is the most likely biological reason based on NCERT principles?

A The specific methanogens required to produce methane from cellulosic material are absent.

B The system is operating optimally for a gobar gas plant.

C The fermentation is being conducted by strict anaerobic bacteria.

D The temperature is too low for hydrogen sulphide production.

💡 Short Explanation

Methane production requires methanogens. If methane is missing, the methanogenic microbes are likely missing or inactive. Carbon dioxide is a common byproduct of general fermentation, but methane requires specialized archaea.

✅ Correct Answer Explanation

Methanogens (like Methanobacterium) are the specific microorganisms responsible for converting organic acids and other intermediate fermentation products into methane. → If the system yields only CO2., it indicates that the initial breakdown of organic matter is occurring, but the final stage—methanogenesis—is not taking place, typically due to the absence or inhibition of methanogenic populations.

❓ Why Other Options Are Incorrect

Option A → If it were optimal, it would yield methane.
Option C → Methanogens are strict anaerobes; this doesn't explain the lack of methane.
Option D → While temperature affects rates, the primary cause of a lack of product is the absence of the producer.

🎯 Strategy

Used: Elimination

Application: Knowing that methanogens are the only producers of methane in this system.

Final Logic: Absence of the product (methane) implies absence of the producer (methanogens).

🧠 Memory Trick

Methane = Methanogens needed.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biogas/Methanogens

2 Consider the following statements regarding microbes as a fuel source:
I. The primary gas produced depends heavily on both the microbes present and the organic substrates utilized.
II. Cheese making and beverage production yield exactly the same methane-rich gas as a biogas plant.
III. Gobar gas is an inflammable energy source derived from microbial metabolism.
Which statements are correct?

A I and II only

B II and III only

C I, II, and III

D I and III only

💡 Short Explanation

Statement I: Correct (Microbe-Substrate specificity). Statement II: Incorrect (Cheese/beverages don't produce methane). Statement III: Correct (Biogas is inflammable).

✅ Correct Answer Explanation

I is correct: Microbial metabolism is specific; the substrate and the microbe determine the gaseous byproduct. → II is incorrect: Cheese and beverage production (e.g., fermentation for ethanol or lactic acid) do not produce methane. → III is correct: Biogas (gobar gas) is primarily methane and is highly inflammable.

❓ Why Other Options Are Incorrect

Options A, B, C → All include the false statement II.

🎯 Strategy

Used: Substitution

Application: Identifying that Statement II contradicts the biological facts of non-methanogenic fermentations.

Final Logic: Since II is false, only C remains.

🧠 Memory Trick

Biogas = Burns; Cheese = Curd (No gas).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biogas Basics

3 Arrange the biological processes leading to energy production in a biogas plant:
1. Methane, CO2, and H2 are actively synthesized.
2. Anaerobic conditions are established in a deep concrete tank.
3. Methanogens begin acting on the cellulosic material in the dung.
4. Biogas accumulates, causing the floating cover to rise.

A 3, 2, 1, 4

B 2, 3, 1, 4

C 1, 3, 2, 4

D 2, 1, 3, 4

💡 Short Explanation

Establish environment (2). Introduce/Start action (3). Synthesize gases (1). Gas collection (4).

✅ Correct Answer Explanation

The plant must first be sealed to create anaerobic conditions (2). → Once anaerobic, methanogens start breaking down the organic material (3). → This metabolism produces the gas mixture (1). → Finally, the gas collects and lifts the floating holder (4).

❓ Why Other Options Are Incorrect

Options A, C, D → Misorder the sequence of environmental setup and biological action.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: The logical sequence of "Condition → Action → Product → Effect."

Final Logic: You cannot have microbial action without the correct anaerobic environment.

🧠 Memory Trick

Anaerobic → Action → Product → Pressure.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biogas Plant Structure/Operation

4 Which of the following scenarios would NOT be associated with the natural habitat or biological functioning of Methanobacterium?

A Flourishing in the anaerobic sludge digesters of a sewage treatment plant.

B Breaking down complex cellulose in the rumen of a cow.

C Rapidly oxidizing organic matter in the highly aerated primary settling tank.

D Producing a mixture of inflammable gases from animal dung.

💡 Short Explanation

Methanogens are obligate anaerobes. They cannot survive/function in aerobic tanks. Aerated tanks are for aerobic bacteria.

✅ Correct Answer Explanation

Methanobacterium are obligate anaerobes. → "Highly aerated" environments contain oxygen, which is toxic to methanogens. → Primary settling tanks are typically non-aerated, but even if they were, oxidation of organic matter in such tanks is an aerobic process, not the work of methanogens.

❓ Why Other Options Are Incorrect

Options A, B, D → All describe documented niches/functions of methanogens.

🎯 Strategy

Used: Extreme Word Filter

Application: Identifying "highly aerated" as the contradiction to "anaerobic."

Final Logic: Methanogens and aerated environments are mutually exclusive.

🧠 Memory Trick

Aerated = Absent Methanogens.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Methanogen Biology

📄 Passage

These bacteria are commonly found in the anaerobic sludge during sewage treatment. These bacteria are also present in the rumen (a part of stomach) of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen. In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle. Do you think we, human beings, are able to digest the celluose present in our foods?

Based on the passage, what is the fundamental symbiotic advantage provided by methanogens residing in the rumen of cattle?

A They act as a direct fuel source for the cattle's respiratory system.

B They facilitate the breakdown of complex cellulosic materials that the cattle ingest.

C They actively protect the cattle from viral respiratory infections.

D They synthesize artificial chemicals to replace natural predation.

💡 Short Explanation

Passage says: "help in the breakdown of cellulose." Cellulose is the cattle's main food. This is the symbiotic advantage.

✅ Correct Answer Explanation

Cattle consume large amounts of plant matter (cellulose). → Mammals (including cattle) cannot produce the cellulase enzyme to digest cellulose directly. → Symbiotic methanogens in the rumen perform this breakdown, providing nutrients to the cattle.

❓ Why Other Options Are Incorrect

Option A → They provide energy to the bacteria and the cow's metabolic pathways, not the "respiratory system."
Option C → Not mentioned in the text.
Option D → Not mentioned in the text.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Directly matching the text's description of "help in the breakdown of cellulose."

Final Logic: Digestion of cellulose is the primary nutritional service provided by rumen microbes.

🧠 Memory Trick

Rumen Microbes = Real Meal-makers (for cellulose).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Cattle Rumen Association

📄 Passage

According to the text, why are these rumen bacteria considered critical to cattle nutrition, contrasting sharply with human digestion?

A Humans possess identical bacteria but do not eat cellulose.

B Cattle rely on these bacteria to digest cellulose, a metabolic capability that human digestion entirely lacks.

C Humans use these bacteria exclusively to ferment dough and cheese.

D Cattle use the bacteria to produce antibiotics within the rumen.

💡 Short Explanation

Cattle have rumen + bacteria for cellulose. Humans don't have rumen + bacteria for cellulose. Cellulose digestion is unique to the ruminant system.

✅ Correct Answer Explanation

The breakdown of cellulose is essential for herbivores like cattle. → Humans lack both the rumen chamber and the symbiotic cellulolytic bacteria. → This is a fundamental biological contrast between ruminant and human digestive physiology.

❓ Why Other Options Are Incorrect

Option A → Humans do not have identical cellulolytic bacteria in their gut.
Option C → These bacteria are not involved in dough/cheese.
Option D → Not a stated role of rumen bacteria in the text.

🎯 Strategy

Used: Elimination

Application: Contrasting digestive physiology (Herbivore/Ruminant vs. Monogastric).

Final Logic: The metabolic capability to digest cellulose is the differentiator between ruminants and humans.

🧠 Memory Trick

Ruminant = Real Cellulose-digester.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Cattle Rumen Association

7 Match the following components of gobar gas production with their functional descriptions:

Column 1	Column 2
1. Gobar	a. An inflammable mixture used for lighting
2. Biogas	b. Excreta rich in cellulose-degrading microbes
3. Spent Slurry	c. Anaerobic agent driving the fermentation
4. Methanogen	d. Nutrient-rich leftover used as fertilizer

A 1-b, 2-c, 3-d, 4-a

B 1-a, 2-b, 3-c, 4-d

C 1-d, 2-c, 3-a, 4-b

D 1-b, 2-a, 3-d, 4-c

💡 Short Explanation

Gobar = Dung with microbes (b). Biogas = Inflammable gas (a). Slurry = Fertilizer byproduct (d). Methanogen = Anaerobic agent (c).

✅ Correct Answer Explanation

All mappings in A correctly align the material with its biological or industrial role according to NCERT.

❓ Why Other Options Are Incorrect

Options A, B, C → Misalign the components; for example, they define Biogas as excreta or Methanogens as Fertilizer.

🎯 Strategy

Used: Option Grouping

Application: Grouping the obvious pairs (Biogas/Lighting and Slurry/Fertilizer).

Final Logic: Matching unambiguous terms eliminates all options except D.

🧠 Memory Trick

Gobar = Great Bacteria (b).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Gobar Gas Materials

8 From an operational standpoint, why is cattle dung converted into a "slurry" before being fed into the concrete tank of a biogas plant?

A To instantly separate the methane gas from the solid waste before entering the tank.

B To provide a uniform, aqueous medium that facilitates optimal anaerobic microbial breakdown.

C To completely sterilize the dung and remove all existing bacteria.

D To prevent the floating cover from rising too quickly.

💡 Short Explanation

Microbes need a medium to interact with substrate. Liquid/Slurry ensures even distribution. Facilitates anaerobic conditions.

✅ Correct Answer Explanation

Microorganisms require a fluid environment to migrate, consume substrate, and interact effectively. → Converting solid dung into a slurry ensures uniform distribution of organic matter and provides the aqueous environment necessary for the metabolic activity of anaerobic bacteria.

❓ Why Other Options Are Incorrect

Option A → Gas is produced inside the tank, not separated before.
Option C → The slurry contains the bacteria needed; it should not be sterilized.
Option D → The cover rise is a desired result of gas production, not something to be prevented.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Understanding the physics and biology of liquid-phase fermentation.

Final Logic: A liquid medium is necessary for optimal microbial metabolic rate.

🧠 Memory Trick

Slurry = Smooth Spread.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Slurry Feed

9 Which of the following is NOT an accurate biological or structural reason for constructing the biogas concrete tank 10-15 feet deep?

A To provide a sufficiently large volume to collect bio-wastes and dung slurry.

B To safely contain the rising pressure of the produced gas beneath the floating holder.

C To help maintain the anaerobic conditions required by the methanogens at the bottom.

D To allow deep penetration of sunlight necessary for the photosynthetic activity of methanogens.

💡 Short Explanation

Methanogens are NOT photosynthetic. Sunlight is not needed. The process is anaerobic.

✅ Correct Answer Explanation

Methanogens are heterotrophic (chemo-organotrophic) bacteria, not photosynthetic. They do not require sunlight. → Sunlight does not penetrate deeply into a concrete tank, and this is not a design criterion for biogas plants.

❓ Why Other Options Are Incorrect

Options A, B, C → All are sound logical reasons for the dimensions or the operational needs of the tank.

🎯 Strategy

Used: Elimination

Application: Recognizing that "photosynthetic" is a fundamental biological error in relation to methanogens.

Final Logic: Since methanogens are not photosynthetic, any statement claiming they are is false.

🧠 Memory Trick

Methanogens = Metabolic (Not light-dependent).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biogas Plant Structure

10 During a routine inspection, the floating cover of a rural biogas plant is observed to be steadily rising. What key biological deduction can be made from this physical observation?

A The concrete tank has developed a severe water leak.

B Aerobic bacteria are consuming the available oxygen and expanding the tank.

C Anaerobic microbes are actively metabolizing the slurry and releasing an inflammable gaseous mixture.

D The spent slurry is clogging the outlet pipe, causing waste backup.

💡 Short Explanation

Rising cover = Gas production. Gas production = Anaerobic metabolism. This is the proof of a working plant.

✅ Correct Answer Explanation

The rising of the gas holder is the visual indicator of accumulated biogas. → Biogas is generated by the metabolic activity of anaerobic microbes, specifically methanogens. → Therefore, a rising cover confirms the successful anaerobic fermentation of organic material.

❓ Why Other Options Are Incorrect

Option A → A leak would cause the cover to sink as gas escapes.
Option B → Aerobic activity does not typically produce large volumes of gas causing structural movement in this context.
Option D → Clogging would stop flow, not lift the gas holder.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Linking physical observation (movement of cover) to biological process (anaerobic respiration).

Final Logic: If the cover is rising, gas is accumulating; if gas is accumulating, the anaerobic process is working.

🧠 Memory Trick

Rising = Reaction working.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Floating Gas Holder

11 Arrange the sequence of events illustrating the operational mechanism of a biogas plant's outputs:
1. Microbial activity generates a mixture of gases.
2. Biogas is forced through the connected supply pipe outlet.
3. The floating gas holder rises due to accumulated gas pressure.
4. The gas is supplied to nearby houses for cooking and lighting.

A 3, 1, 2, 4

B 1, 2, 3, 4

C 1, 3, 2, 4

D 2, 1, 3, 4

💡 Short Explanation

Generate gas (1). Gas pressure builds/Lifts cover (3). Pushed through pipe (2). Used for cooking/lighting (4).

✅ Correct Answer Explanation

Microbial activity produces the gas (1). → As gas accumulates, the pressure lifts the floating holder (3). → The pressurized gas is then forced through the outlet pipe (2). → Finally, the gas reaches the destination for use (4).

❓ Why Other Options Are Incorrect

Options A, B, D → Misorder the cause-effect relationship between gas production, pressure, and flow.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: The logical sequence of gas generation and distribution.

Final Logic: Production leads to pressure, which leads to movement, which leads to utility.

🧠 Memory Trick

Generate → Lift → Pipe → Use.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Plant Operations

12 An agricultural scientist evaluates the spent slurry discharged from a biogas plant. What strongly justifies its direct use as a high-quality field fertilizer?

A It contains high levels of concentrated, undigested synthetic chemicals.

B It is completely stripped of all nitrogen and phosphorus during gas production.

C It acts as a powerful weedicide that destroys all field fauna.

D It is rich in organic nutrients remaining after microbes have extracted the carbon-based energy.

💡 Short Explanation

Slurry contains residue (nitrogen/phosphorus/organic matter). Microbes only extract carbon-energy. It is ideal soil enrichment.

✅ Correct Answer Explanation

Anaerobic digestion primarily converts carbonaceous compounds (cellulose) into methane. → Essential plant nutrients (Nitrogen, Phosphorus, Potassium) remain in the slurry, making it an excellent fertilizer.

❓ Why Other Options Are Incorrect

Option A → It is organic, not synthetic.
Option B → It is rich in these nutrients, not stripped of them.
Option C → It is a fertilizer, not a weedicide.

🎯 Strategy

Used: Elimination

Application: Knowing the definition of fertilizer (nutrient source).

Final Logic: The process concentrates nutrients for plant growth.

🧠 Memory Trick

Slurry = Soil's Salvation.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Fertilizer Byproducts

13 Which of the following is NOT a reason why the technology promoted by IARI is highly successful in rural Indian areas?

A Cattle are used for a variety of purposes, making dung abundantly available.

B Rural households require accessible energy sources for cooking and lighting.

C The spent slurry perfectly supports agricultural fertilizer needs.

D Rural areas produce massive quantities of sterile, bacteria-free dung.

💡 Short Explanation

Dung is full of bacteria (it is not sterile). The bacteria are actually needed for the plant to work. Statement C is factually false.

✅ Correct Answer Explanation

Dung is rich in bacteria (methanogens). Calling it "sterile" or "bacteria-free" is scientifically incorrect and contrary to the principles of biogas production.

❓ Why Other Options Are Incorrect

Options A, B, C → All identify valid reasons for the adoption and success of biogas technology in India.

🎯 Strategy

Used: Extreme Word Filter

Application: Identifying "sterile" as a biological absurdity in the context of animal waste.

Final Logic: Biogas relies on non-sterile, microbe-rich input.

🧠 Memory Trick

Sterile = Silly statement.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Indian Development Agencies

14 Consider the following statements regarding the institutional development of biogas in India:
I. KVIC and IARI primarily developed this technology to manage urban industrial waste.
II. The technology was developed in India mainly due to the collaborative efforts of IARI and KVIC.
III. Encouraging school students to visit nearby biogas plants is recommended to learn from actual managers.
Which statements accurately reflect the NCERT text?

A II and III only

B I and II only

C I and III only

D I, II, and III

💡 Short Explanation

IARI/KVIC developed it for rural areas, not urban/industrial (I is false). II and III are correct NCERT claims.

✅ Correct Answer Explanation

Statement I is incorrect: The focus was specifically on rural development, not urban/industrial waste. → Statements II and III are standard NCERT statements concerning the history and educational outreach of biogas tech.

❓ Why Other Options Are Incorrect

Options B, C, D → All include the incorrect statement I.

🎯 Strategy

Used: Substitution

Application: Recalling the "rural" focus of the KVIC/IARI mandate.

Final Logic: Since the mandate was rural, Statement I must be false.

🧠 Memory Trick

Rural Rises (KVIC/IARI).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Indian Development Agencies

15 How does the organic farming concept of "natural predation" fundamentally conflict with conventional chemical pest control?

A Natural predation targets only beneficial insects, whereas chemicals target only pests.

B Chemical control relies on a complex system of checks and balances, unlike natural predation.

C Chemical farming indiscriminately kills both useful and harmful life forms, disrupting the natural predator-prey balance.

D Natural predation introduces highly toxic biological agents into the groundwater.

💡 Short Explanation

Chemicals = indiscriminate toxins. Biocontrol = specific/balanced. Chemicals destroy the "checks and balances."

✅ Correct Answer Explanation

Conventional chemical pesticides are broad-spectrum, meaning they kill both pests and the beneficial insects (predators) that manage them. → This destruction of the predator-prey balance is why natural predation (biocontrol) is preferred in organic farming.

❓ Why Other Options Are Incorrect

Options A, B, D → All contradict the passage's logic.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: The passage emphasizes ecosystem balance.

Final Logic: The indiscriminate nature of chemicals is the core argument against them.

🧠 Memory Trick

Chemicals = Carnage (indiscriminate).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biocontrol Foundations

16 According to the organic farming approach detailed in the text, what is the ecological reasoning behind maintaining pests at "manageable levels" rather than completely eradicating them?

A Eradicating them is too expensive for rural farmers.

B Their total eradication would cause the starvation and decline of beneficial predatory insects that rely on them.

C Pests are required to cross-pollinate all major crop plants.

D Eradication would cause the pests to immediately mutate into chemical-resistant super-bugs.

💡 Short Explanation

Predatory insects eat pests. If pests disappear, predators starve/leave. The system collapses.

✅ Correct Answer Explanation

Predator-prey systems are tightly linked. Beneficial insects (predators) require a population of pests (prey) to survive. → Total eradication of the prey leads to the loss of the beneficial predator, creating an unstable ecosystem.

❓ Why Other Options Are Incorrect

Options A, C, D → These are not the ecological reasons cited in the text for maintaining pest populations.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Understanding predator-prey dynamics described in the passage.

Final Logic: Predators need their food source (prey) to remain present.

🧠 Memory Trick

Predators Need Prey.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Pest Management Systems

17 Match the biocontrol agents/concepts with their specific targets or outcomes:

Column 1	Column 2
1. Ladybird	a. Reduces dependence on toxic substances
2. Dragonfly	b. Useful to get rid of aphids
3. Biocontrol approach	c. Useful to get rid of mosquitoes
4. Chemical pesticides	d. Indiscriminately kill beneficial and harmful life forms

A 1-b, 2-a, 3-c, 4-d

B 1-c, 2-b, 3-d, 4-a

C 1-b, 2-c, 3-a, 4-d

D 1-a, 2-c, 3-b, 4-d

💡 Short Explanation

Ladybird = Aphids (b). Dragonfly = Mosquitoes (c). Biocontrol = Reduces toxic dependency (a). Chemicals = Indiscriminate killing (d).

✅ Correct Answer Explanation

All mappings in C correctly correlate the insect or approach with its biological role or consequence according to the text.

❓ Why Other Options Are Incorrect

Options A, B, D → Misalign the biological agents with their targets (e.g., swapping Ladybird and Dragonfly targets).

🎯 Strategy

Used: Option Grouping

Application: Matching the most distinct pairs (Ladybird/Aphid and Chemical/Indiscriminate).

Final Logic: The only pairing that matches the known biology is C.

🧠 Memory Trick

Ladybird = Aphids.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Familiar Biocontrol Insects

18 Which of the following is NOT an advantage of using dragonflies to control mosquito populations in a given habitat?

A It constitutes a living, vibrant ecosystem check on the pest.

B It significantly reduces the dependence on chemical mosquito repellents and sprays.

C It acts as a highly toxic chemical agent that permanently poisons the mosquito breeding grounds.

D It utilizes natural predation rather than introducing toxic external substances.

💡 Short Explanation

Biocontrol is not chemical. It is not a toxic agent. It is a living predator (Dragonfly).

✅ Correct Answer Explanation

Dragonflies are biological agents (predators), not toxic chemicals. → The term "toxic chemical agent" is the opposite of the definition of biocontrol.

❓ Why Other Options Are Incorrect

Options A, B, D → These accurately list the benefits of using biological control (Dragonflies).

🎯 Strategy

Used: Extreme Word Filter

Application: Identifying "highly toxic chemical agent" as a contradiction to "Biocontrol."

Final Logic: Biological agents are living, not poisonous chemicals.

🧠 Memory Trick

Bioconrol = Bug (Not Chemical).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Dragonflies vs Mosquitoes

19 Why is the biocontrol agent Bacillus thuringiensis (Bt) considered highly safe for widespread deployment on vulnerable fruit trees?

A It specifically targets and kills insect caterpillars while leaving other beneficial insects entirely unharmed.

B It forms a symbiotic relationship with the fruit tree roots, enhancing water uptake.

C It rapidly eradicates all insect life forms in the orchard, preventing any future infestations.

D It is a chemical that naturally degrades into oxygen within hours of spraying.

💡 Short Explanation

Bt is a selective toxin. It targets specific larvae (caterpillars). It is not a general killer.

✅ Correct Answer Explanation

Bt is a biocontrol agent specifically noted for its selectivity. → Its toxicity is limited to specific insect groups (like lepidopteran larvae/caterpillars) because of the required alkaline gut conditions for activation. → This specificity makes it "safe" compared to general-spectrum chemicals.

❓ Why Other Options Are Incorrect

Option B → Not its function.
Option C → It does not eradicate "all insect life."
Option D → It is a biological agent (bacteria), not a chemical that degrades into oxygen.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: The core benefit of Bt in NCERT is "species specificity."

Final Logic: Selectivity is the hallmark of safe biocontrol.

🧠 Memory Trick

Bt = Balanced Targeting.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbial Control Agents

20 The toxin produced by Bacillus thuringiensis is ingested by a caterpillar but remains functionally inactive until a specific biological condition is met. Where exactly does this toxin get released to become lethal?

A In the vascular tissue of the brassica plant

B In the gut of the insect larvae

C On the external exoskeleton of the caterpillar

D Within the dried spores before mixing with water

💡 Short Explanation

Toxin requires activation. Alkaline gut pH triggers activation. Lethal release happens in the gut.

✅ Correct Answer Explanation

Bt toxin crystals (protoxins) are ingested. → Upon reaching the midgut of the susceptible larvae, the alkaline pH causes the crystals to solubilize and release the active toxin. → This activated toxin destroys the gut epithelium.

❓ Why Other Options Are Incorrect

Option A, C, D → These locations do not provide the necessary alkaline pH required for activation.

🎯 Strategy

Used: Substitution

Application: Recalling the mechanism of action from NCERT (Bt toxin activation).

Final Logic: Gut pH is the biological key to releasing the toxin.

🧠 Memory Trick

Bt = Breaks The gut.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbial Control Agents

CUET UG Biology Booster Test 2-Microbes in Energy and Biocontrol

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